SybilLimit: A Near-Optimal Social Network Defense against Sybil Attacks

Abstract

Decentralized distributed systems such as peer-to-peer systems are particularly vulnerable to sybil attacks, where a malicious user pretends to have multiple identities (called sybil nodes). Without a trusted central authority, defending against sybil attacks is quite challenging. Among the small number of decentralized approaches, our recent SybilGuard protocol [42] leverages a key insight on social networks to bound the number of sybil nodes accepted. Although its direction is promising, SybilGuard can allow a large number of sybil nodes to be accepted. Furthermore, SybilGuard assumes that social networks are fast mixing, which has never been confirmed in the real world.This paper presents the novel SybilLimit protocol that leverages the same insight as SybilGuard but offers dramatically improved and near-optimal guarantees. The number of sybil nodes accepted is reduced by a factor of Θ( √ n), or around 200 times in our experiments for a million-node system. We further prove that SybilLimit's guarantee is at most a log n factor away from optimal, when considering approaches based on fast-mixing social networks. Finally, based on three large-scale real-world social networks, we provide the first evidence that real-world social networks are indeed fast mixing. This validates the fundamental assumption behind SybilLimit's and SybilGuard's approach.

SocialFilter: Introducing social trust to collaborative spam mitigation

“…Identity uniqueness. The repository defends against Sybil attacks [10] by exploiting the fact that OSNs can be used for resource testing [18,24,27]. The test in question is a Sybil attacker's ability to create and sustain acquaintances.…”

“…The test in question is a Sybil attacker's ability to create and sustain acquaintances. Using a SybilLimit-based [27] technique ( §3.2,) the OSN provider assigns an identity uniqueness value to each node. This value quantifies the system's belief in that node not being a Sybil.…”

“…Using a SybilLimit-like [27] technique, OSNs can approximate the belief that a node's identity is not a Sybil. We refer to this belief as identity uniqueness.…”

“…Each node is associated with its administrator's identity. The identity uniqueness of a node is determined via the social network of administrators using a SybilLimit-based technique [27].…”

False-Name-Proofness in Social Networks

“…The basic intuition that the creation of false identities in a social network results in suspiciously small vertex cuts has previously been explored in several papers, in the context of peer-to-peer networks [18,17] and web spam detection [2,3,6,7,13].…”